The process of forming connection holes in the dielectric layer by etching and subsequently depositing conductive materials in the connection holes is widely used in the semiconductor manufacturing process. The connection holes can be used in the electric connection with the gate electrode, the source electrode and the drain electrode, the electric connection between the dielectric layers and the electric connection in the back-end package process.
FIGS. 1 to 4 illustrate a conventional method of forming connection holes in the back-end aluminum interconnection process. Referring to FIG. 1, the method comprises providing a semiconductor substrate with a metal layer 101 on the surface thereof; forming an etching stopper layer 102, a first DARC (dielectric anti-reflective coating) layer 103, an interlayer dielectric layer 104 and a second DARC layer 105 successively on the surface of the metal layer 101; forming a photoresist pattern 106 on the second DARC layer 105, wherein the openings of the photoresist pattern define the connection holes; referring to FIG. 2, etching the second DARC layer 105 using the photoresist pattern as a mask until exposing the interlayer dielectric layer 104; afterwards, as shown in FIG. 3, continue to etching the interlayer dielectric layer 104 until exposing the first DARC layer 103; then applying over-etching and stopping on the etching stopper layer 102. In the method of forming connection holes mentioned above, for example, the material of the metal layer 101 is Al (aluminum), the material of the etching stopper layer 102 is TiN (titanium nitride), the material of the first DARC layer 103 and the second DARC layer 105 is SiON (silicon oxynitride), and the material of the interlayer dielectric layer 104 is SiOX (silicon oxide). The etching is a plasma etching.
Generally, more than one connection holes are required to form in the interlayer dielectric layer 104 and the diameters of the connection holes may differs according to the process design. Due to the loading effect during the plasma etching, the reactive species which cause the etching reaction may enter into the bottom of the openings of various sizes with different difficulty levels, which leads to the different etching rates in the connection holes. Specifically, the connection holes having smaller diameters make it difficult for the reactive species to get into the bottom thereof and the etching rate therein is low, while the connection holes having larger diameters make it easy for the reactive species to get into the bottom thereof and the etching rate therein is high. When the etching process is applied to the connection holes with great differences in diameter (such as three to four folds), the connection holes having larger diameters may even extend through the etching stopper layer (TiN) 102 to expose the metal layer 101, which causes the great variations of the connecting resistance and affects the performance of the back-end wirings.